A circuit for current multiplication is illustrated in FIG. 1. Based on translinear loop equations, the following relationships hold:Vbe1+Vbe2 +Vbe3=Vbe4+Vbe5+Vbe6,  (1)Ic1*Ic2*Ic3=Ic4*Ic5*Ic6, and  (2)Iout=Ic6=Ic1*Ic2/Ic5  (3)where Vbe1 represents the voltage measured between the anode terminal and cathode of a first diode 110 (Q1); Vbe2 represents the voltage between the base and emitter of a first transistor 120 (Q2); Vbe3 represents the voltage between the base and emitter of a second transistor 130 (Q3); Vbe4 represents the voltage between the anode and the cathode of a second diode 140 (Q4); Vbe5 represents the voltage between the base and emitter electrode of a third transistor 150 (Q5); and Vbe6 represents the voltage between the base and emitter of a fourth transistor 160 (Q6). In addition, Ic6 represents the current measured at the cathode of the first diode 110 (Q1); Ic2 represents the current at the collector electrode of the first transistor 120 (Q2); Ic3 represents the current at the collector of the second transistor 130 (Q3); Ic4 represents the current at the cathode of the second diode 140 (Q4); Ic5 represents the current at the collector of the third transistor 150 (Q5); and Ic6 represents the current at the collector of the fourth transistor 160 (Q6).
Although the circuit presented in FIG. 1 produces an output current Iout that is a multiple of its input current, its output current is not necessarily a squared input current. Having a circuit that produces a squared input current has a number of practical applications. For example, a logarithmic amplifier for measuring the power of an RF signal often requires that the amplifier exhibit conformity to the known true square law over a broad dynamic range and be relatively independent of temperature. The subject matter described herein presents circuitry having these characteristics.